An image sensor is a semiconductor device that converts an optical image to an electrical signal. Image sensors are generally classified as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) image sensor (CIS).
The CIS includes a photodiode and a MOS transistor in a unit pixel. The CIS sequentially detects electric signals of unit pixels in a switching manner to realize an image.
As the design rule in the CIS decreases gradually, the size of a unit pixel also decreases, which may cause the photosensitivity to be decreased. To increase the photosensitivity, a microlens is often formed on a color filter.
However, an additional structure, such as a metal line or the like, existing on a light path from the microlens to a photodiode, may cause light diffraction, light scattering, or the like, thereby decreasing the photosensitivity of the image sensor.